The present invention relates to an improved fuse structure connecting first level and second level interconnections in an inter-layer insulator in a semiconductor device, wherein the fuse structure is to be electrically disconnected to shift a defective circuit into a redundancy circuit upon receipt of an irradiation of a pulse laser beam.
In wafer checking processes, a chip verified as defective is required to change a defective circuit in the chip into a redundancy circuit by an irradiation of a pulse laser beam onto a fuse in the chip for electrical disconnection of the fuse. In a semiconductor device having a memory of a large capacity, redundancy bit cells are previously formed in memory cell arrays so that if a bit cell is verified as defective in checking process, then the defective bit cell is changed into a redundancy bit cell by an irradiation of a pulse laser beam onto a fuse connected to the defective bit cell for electrical disconnection of the fuse. As a result, it is possible to salvage the defective chip, thereby increasing the yield thereof.
The increase in yield of the chips is one of the most important issues to be realized particularly as the high density integration of the semiconductor devices and the scale of the chip have increased. In this circumstances, it is effective that the fuse is electrically disconnected to change the defective circuit in the chip into the redundancy circuit to relief the defective chip, thereby increasing the yield thereof.
In the past, the conventional fuse often comprises a polysilicon layer, a part of which serves as a gate electrode of a MOS field effect transistor. In recent years, however, in order to respond to the multi-level interconnection semiconductor devices, there has been proposed a fuse structure comprising a metal plug in a via hole for electrically connecting first level and second level interconnections. This technique will be disclosed with reference to FIGS. 1A, 1B, 2A and 2B. FIG. 1A is a fragmentary plan view illustrative of a first conventional fuse structure comprising a metal plug connecting first and second level interconnections in an inter-layer insulator before the fuse structure is disconnected by an irradiation of a laser beam. FIG. 1B is a fragmentary cross sectional elevation view illustrative of the first conventional fuse structure of FIG. 1A taken along an IB--IB line in FIG. 1A. FIG. 2A is a fragmentary plan view illustrative of a first conventional fuse structure comprising a metal plug connecting first and second level interconnections in an inter-layer insulator after the fuse structure was disconnected by an irradiation of a laser beam. FIG. 2B is a fragmentary cross sectional elevation view illustrative of the first conventional fuse structure of FIG. 2A taken along an IIB--IIB line in FIG. 2A.
A first level interconnection 102 extends over a first inter-layer insulator 101. A second inter-layer insulator 103 overlies the first interlayer insulator 101 and the first level interconnection 102. The second inter-layer insulator 103 has a via hole within which a metal plug 105 is filled. Namely, the metal plug 105 is buried within the second inter-layer insulator 103. The metal plug 105 is electrically connected to a first connecting part of the first level interconnection. A second level interconnection 104 extends over the second inter-layer insulator 103 so that a second connecting part of the second level interconnection 104 is positioned over the via hole, whereby the second connecting part of the second level interconnection 104 is electrically connected to the metal plug 105. As a result, the first level interconnection 102 and the second level interconnection 104 are electrically connected through the metal plug 105 to each other. The first level interconnection 102 and the second level interconnection 104 extend in anti-parallel directions, that is, parallel but oppositely directed. The first level interconnection 102 and the second level interconnection 104 have the same longitudinal direction. A first longitudinal axis of the first level interconnection 102 is aligned with a second longitudinal axis of the second level interconnection 104 in a plan view. The second connecting part of the second level interconnection 104 overlaps the first connecting part of the first level interconnection 102 in the plan view. A third inter-layer insulator 107 overlies the second inter-layer insulator 103 and the second level interconnection 104, whereby the second level interconnection 4 is buried in the third level interconnection 107. A passivation film 109 extends over the third inter-layer insulator 107.
A recess 108 is formed over the second connecting part of the second level interconnection 104, wherein the recess 108 extends through the passivation film 109 and into the upper region of the third inter-layer insulator 107 so that the bottom of the recess 108 is separated by a thin wall of the third inter-layer insulator 107 from the second connecting part of the second level interconnection 104. The plan size of the recess 108 is sufficiently larger than the second connecting part of the second level interconnection 104.
The first level interconnection 102 and the second level interconnection 104 are connected to circuits for selecting a redundancy circuit, so that, upon electrical disconnection between the first level interconnection 102 and the second level interconnection 104, the defective circuit comes non-selected whilst the redundancy circuit comes selected. The electrical disconnection between the first level interconnection 102 and the second level interconnection 104 may be obtained by irradiation of a pulse laser beam toward the second connecting part of the second level interconnection 104 as a target in order to cause a rapid and explosive evaporation of the second connecting part of the second level interconnection 104.
With reference to FIGS. 2A and 2B, a pulse laser beam is irradiated toward the second connecting part of the second level interconnection 104 as a target so that the pulse laser beam penetrates through the recess 108 and the third inter-layer insulator 107 to be irradiated onto the second connecting part of the second level interconnection 104, where the pulse laser beam is absorbed by the second connecting part of the second level interconnection 104. Namely, the second connecting part of the second level interconnection 104 receives a large thermal energy, so that the second connecting part of the second level interconnection 104 shows a rapid and explosive evaporation, whereby the thin walls of the third inter-layer insulator 107 between the second connecting part of the second level interconnection 104 and the recess 108 are broken by the above explosive evaporation of the second connecting part of the second level interconnection 104. As a result of the explosive evaporation of the second connecting part of the second level interconnection 104, the explosively evaporated material such as aluminum of the second connecting part of the second level interconnection 104 is explosively blown through the broken thin wall up to the recess 108, whereby the evaporated material is then deposited on side walls of a hole over the metal plug 105 formed by the explosive evaporation. As a result, the metal plug 105 is electrically disconnected from the second level interconnection 104 missing the second connecting part. Therefore, the second level interconnection 104 is electrically disconnected from the first level interconnection 102. Upon electrical disconnection between the first level interconnection 102 and the second level interconnection 104, the defective circuit comes non-selected whilst the redundancy circuit comes selected.
The existence of the recess 108 over the second connecting part of the second level interconnection 104 but separated by the thin wall of the third inter-layer insulator 107 from the second connecting part of the second level interconnection 104 allows that, upon irradiation of the pulse laser beam toward the second connecting part of the second level interconnection 104, the second connecting part of the second level interconnection 104 is explosively evaporated and then the evaporated material of the second connecting part of the second level interconnection 104 is explosively blown through the broken thin wall of the third inter-layer insulator 107 up to the recess 108 before the evaporated material is deposited onto the side walls of the hole made by explosive evaporation, whilst substantially no evaporated material of the second connecting part of the second level interconnection 104 resides over the metal plug 105, resulting in a certain electrical disconnection between the second level interconnection 104 is electrically disconnected from the first level interconnection 102.
The above first conventional fuse structure has the following disadvantages. Each of the first inter-layer insulator 101, the second inter-layer insulator 103, and the third inter-layer insulator 107 is made by both a high density plasma enhanced chemical vapor deposition and subsequent chemical mechanical polishing method to form a planar surface thereof, in order to obtain a global planarization in a short time period. Further, in order to reduce the parasitic capacitance between the first level and second level interconnections 102 and 104, each of the first inter-layer insulator 101, the second inter-layer insulator 103, and the third inter-layer insulator 107 is made of fluorine containing silicon oxide having a low dielectric constant but a high hygroscopicity. The absence of the passivation film 109 having relatively low hygroscopicity over the second connecting part of the second level interconnection 104 allows a substantive permeation of moisture into the third inter-layer insulator 107 shown through the recess 108, whereby the second level interconnection 104, the metal plug 105 and the first level interconnection 102 are exposed to the permeation of the moisture, whereby the second level interconnection 104, the metal plug 105 and the first level interconnection 102 may show erosion due to the moisture permeation.
In order to settle the above problem with moisture permeation through the recess, a second conventional fuse structure has also been proposed, which will be described with reference to FIGS. 3A, 3B, 4A and 4B. FIG. 3A is a fragmentary plan view illustrative of a second conventional fuse structure comprising a metal plug connecting first and second level interconnections in an inter-layer insulator before the fuse structure is disconnected by an irradiation of a laser beam. FIG. 3B is a fragmentary cross sectional elevation view illustrative of the second conventional fuse structure of FIG. 3A taken along an IIIB--IIIB line in FIG. 3A. FIG. 4A is a fragmentary plan view illustrative of a second conventional fuse structure comprising a metal plug connecting first and second level interconnections in an inter-layer insulator after the fuse structure was disconnected by an irradiation of a laser beam. FIG. 4B is a fragmentary cross sectional elevation view illustrative of the second conventional fuse structure of FIG. 4A taken along an IVB--IVB line in FIG. 4A.
A first level interconnection 102 extends over a first inter-layer insulator 101. A second inter-layer insulator 103 overlies the first inter-layer insulator 101 and the first level interconnection 102. The second inter-layer insulator 103 has a via hole within which a metal plug 105 is filled. Namely, the metal plug 105 is buried within the second inter-layer insulator 103. The metal plug 105 is electrically connected to a first connecting part of the first level interconnection. A second level interconnection 104 extends over the second inter-layer insulator 103 so that a second connecting part of the second level interconnection 104 is positioned over the via hole, whereby the second connecting part of the second level interconnection 104 is electrically connected to the metal plug 105. As a result, the first level interconnection 102 and the second level interconnection 104 are electrically connected through the metal plug 105 to each other. The first level interconnection 102 and the second level interconnection 104 extend in anti-parallel directions. The first level interconnection 102 and the second level interconnection 104 have the same longitudinal direction. A first longitudinal axis of the first level interconnection 102 is aligned with a second longitudinal axis of the second level interconnection 104 in a plan view. The second connecting part of the second level interconnection 104 overlaps the first connecting part of the first level interconnection 102 in the plan view. A third inter-layer insulator 107 overlies the second inter-layer insulator 103 and the second level interconnection 104, whereby the second level interconnection 104 is buried in the third level interconnection 107. A passivation film 109 extends over an entire surface of the third inter-layer insulator 107.
In order to settle the above problem with the moisture permeation, no recess is formed over the second connecting part of the second level interconnection 104.
The first level interconnection 102 and the second level interconnection 104 are connected to circuits for selecting a redundancy circuit, so that, upon electrical disconnection between the first level interconnection 102 and the second level interconnection 104, the defective circuit becomes non-selected whilst the redundancy circuit is selected. The electrical disconnection between the first level interconnection 102 and the second level interconnection 104 may be obtained by irradiation of a pulse laser beam toward the second connecting part of the second level interconnection 104 as a target in order to cause a rapid and explosive evaporation of the second connecting part of the second level interconnection 104.
With reference to FIGS. 4A and 4B, a pulse laser beam is irradiated toward the second connecting part of the second level interconnection 104 as a target so that the pulse laser beam penetrates through the passivation film 109 and the third inter-layer insulator 107 to be irradiated onto the second connecting part of the second level interconnection 104, where the pulse laser beam is absorbed by the second connecting part of the second level interconnection 104. Namely, the second connecting part of the second level interconnection 104 receives a large thermal energy, so that the second connecting part of the second level interconnection 104 shows a rapid and explosive evaporation. Since, however, no recess is formed over the second connecting part of the second level interconnection 104, the explosively evaporated material such as aluminum of the second connecting part of the second level interconnection 104 is confined within the space of the second connecting part of the second level interconnection 104, whereby the evaporated material is then deposited on inner walls of the space of the second connecting part of the second level interconnection 104 to reside on the metal plug 105. As a result, the metal plug 105 remains electrically connected through the deposited metal material to the second level interconnection 104 even missing the second connecting part. Therefore, the second level interconnection 104 remains electrically connected from the first level interconnection 102.
In the above circumstances, it had been required to develop a novel fuse structure comprising a metal plug connecting first level and second level interconnections in an inter-layer insulator free from the above problems.